The concept of positive interest rates is straightforward. You take your savings, which you amass by forgoing current consumption — not buying a newer car or making fewer trips to fancy restaurants — and lend them to someone. In exchange for your sacrifice, you receive interest payments.

With negative interest rates, something very different happens: You lend $100 to your neighbor. A year later the neighbor knocks on your door and, with a smile on his face, repays that $100 loan by writing you a check for $95. You had to pay him $5 for forgoing your consumption of $100 for a year! Try to explain this logic to your kids. We tried to explain it to ours and failed, miserably.

Some countries resort to negative interest rates because they want to devalue their currencies. This strategy suffers from what economists call the fallacy of composition: the mistaken assumption that what is true of one member of a group is true for the group as a whole. As a country adopts negative interest rates, its currency will decline against others — arguably stimulating its export sector (at the expense of other countries). But there is absolutely nothing proprietary about this strategy: Other governments will do the same, and in the end all will experience lowered consumption and a higher savings rate.

As we zoom in, things get worse. Let’s start with Europe, the world’s second-largest economy. European political (EU) and monetary (EMU) unions were great experiments that made a lot of sense on paper. Europe, which had roughly the same-size population and economy as the U.S., was at a competitive disadvantage as dozens of currencies embedded extra transaction costs in cross-border trade, and each currency on its own had little chance of competing with the U.S. dollar for reserve currency status.

There were also important noneconomic considerations. Germans were haunted by their past; they had started two world wars in the 20th century, and a united Europe was their way of lowering the risk of future European wars.

Economic and Monetary Union sounded like a very logical marriage of all the significant powers of post–World War II Europe, but the arrangement was never really a marriage. It was more like a civil union. EMU members combined their currencies into one, the euro. They agreed to use the same central bank and thus implicitly guaranteed one another’s debts.

Though treaties put limits on budget deficits (limits that, ironically, Germany was the first to exceed), each country went on spending its money as it wished. Some were relatively frugal (like Germany); others (Portugal, Ireland, Italy, Greece and Spain) went on spending binges, like newly hitched college students who had just gotten their first credit card, with an irresistibly low introductory rate and a free T-shirt.

The European Union is a collection of states that are vastly different from one another. They are separated by culture, language (which impedes labor mobility, resulting in semipermanent labor productivity disparity between countries — think Greece and Germany), economic growth rates, indebtedness and history. Germany, for instance, suffered through hyperinflation in the early 20th century and is thus paranoid about inflation.

Now let’s turn to Brexit, the U.K. referendum on exiting the EU. Ironically, the U.K. doesn’t have half the problems that most EU nations are going through. Because it is not part of EMU, it has retained its currency and its central bank.

The U.K.’s main dissatisfaction with EU membership stems from the immigration issue. Because treaties have turned the EU into a borderless union, when Germany accepted refugees from the Middle East and Northern Africa, it basically made a unilateral decision on behalf of all EU members to accept those refugees to all EU countries. High unemployment, wage stagnation and terrorism are now endemic in the EU, and you can see how the U.K.’s citizenry might have a problem with this.

After the Brexit vote, the financial media lit up with opinions on its consequences for the EU and the global economy. They’ve varied from “Brexit is a nonevent” to “This is a Lehman moment for the global economy,” referring to the Lehman Brothers bankruptcy that almost brought the financial system to a halt in 2008. The arguments on both sides are quite convincing.

The argument for Brexit’s being a nonevent is simple and straightforward. The U.K. maintained its currency, and the pound’s decline in the aftermath of the referendum will help cushion any negative fallout on the British economy. The U.K. and the EU will forge new trade treaties. There is a fear that the EU may impose trade sanctions on U.K., not so much to punish the U.K. but to threaten other EU members that exit will come at a stiff economic cost (effectively turning this voluntary club into a prison). However, the U.K. is a net importer of goods from the EU; thus any sanctions will hurt remaining EU members more than the U.K.

The Lehman moment argument is less simple, but not unimaginable. Brexit may provide the spark that will ignite already gasoline-soaked ground. Though the EU and EMU were supposed to unite Europeans, they may have had the opposite effect — causing a groundswell of nationalism.

In all honesty, we are concerned more about Italy than the U.K. Italy is the third-largest economy in the EU, and its debt stands at 132 percent of GDP, second only to Greece (171 percent). Seventeen percent of Italian bank loans are noncurrent. In the depths of the financial crisis, that number was 5 percent in the U.S. Italian lenders account for nearly half of bad debt in the EU (source: WSJ).

If Italy was not part of EMU, it could just print lire and bail out its banks. But it gave up that luxury when it joined the single currency. To make things worse, in 2014 the EU passed a law that prohibits governments from bailing out their banking systems; thus the shareholders, debtholders and depositors may bear the brunt of the eventual bailout. Unless the EU passes a new law that bends the 2014 law — or the Italian government takes matters into its own hands, violating EU rules — we may see Italian debtholders and depositors hit with the cost of bank bailouts take to the streets and demand “Italexit.”

Given that the situation in Europe is so complex and combustible, we don’t know whether Brexit will be just another match that simply burns out or the one that starts the fire. Will it trigger other exits? Will it slow down EU growth, thus straining an already leveraged system? We don’t know, and nobody does.

But it gets worse, much worse. The numbers also show that every $1 of new debt brought only pennies of GDP growth. In the absence of skyrocketing debt, the Chinese overcapacity bubble, which was already fully inflated pre-2007, would have burst years ago.

As the government continues to engineer growth by borrowing, every yuan of debt will bring less growth. The laws of economics have not been suspended in China. American economist Herbert Stein’s law states that things that cannot go on forever, won’t. When its debt bubble bursts, China will turn from being a tailwind for global growth into a headwind.

This brings us to Japan. It is the most-indebted developed nation in the world, with a debt-to-GDP ratio of more than 230 percent. Japan is the proof of Stein’s law — its economy is still suffering a hangover from what at the time seemed like an endless real estate party (bubble) that lasted from the mid-1980s into the early ’90s. Japan has been on the quantitative easing and endless stimulus bandwagon longer than anyone else and has nothing (well, except a lot of debt) to show for it.

Secondly, we wanted to show you the headwinds we are facing and what we are doing to avoid having them deflate the sails of your portfolio. Summarizing, these headwinds are:

• The risk of lower or negative global economic growth. If we get higher economic growth, we’ll treat that as a bonus.

• Something-flation. Inflation (high interest rates), deflation (low interest rates) or screwflation (higher interest rates and deflation). We don’t know which of these extremes we’ll see and in which order. Nobody does. Despite their eloquence and portrayed confidence, financial commentators arguing one or another extreme point of view on CNBC don’t know either. In fact, the more confident they are, the more dangerous they are. The difference between us and them is that we know we don’t know and are therefore trying to construct an “I don’t know” portfolio that can handle any extremes.

Ultimately, stock valuations will decline.

This is a time for humility and patience. Humility, because saying the words “I don’t know” is difficult for us testosterone-laden alpha male money manager types.

Patience, because most assets today are priced for perfection. They are priced for a confluence of two outcomes: low (or negative) interest rates continuing where they are or declining further, and above-average global economic growth. Both happening at once in the future is extremely unlikely. Take one of them away (only one!), and stock market indexes are overvalued somewhere between a lot and humongously (we don’t even try to quantify superlatives).